Various methods and systems are known in the art for tracking the coordinates of objects involved in medical procedures. Some of these systems are based on transmission and reception of magnetic fields. In some cases, the fields are transmitted by radiators outside the body and received by sensors fixed to an object within the body; whereas in other cases, radiators on the object within the body transmit fields to receivers outside the body. The basic techniques for computing the coordinates of the object based on the sensed fields are similar in either case.
For example, U.S. Pat. Nos. 5,391,199 and 5,443,489 to Ben-Haim, whose disclosures are incorporated herein by reference, describe systems wherein the coordinates of an intrabody probe are determined using one or more field transducers, such as a Hall effect device, coils, or other antennas. Such systems are used for generating location information regarding a medical probe or catheter. A sensor, such as a coil, is placed in the probe and generates signals in response to externally-applied magnetic fields. The magnetic fields are generated by magnetic field transducers, such as radiator coils, fixed to an external reference frame in known, mutually-spaced locations. Alternatively, a transmitting antenna in the probe may generate the magnetic fields, which are then sensed by receivers outside the body.
PCT Patent Publication WO 96/05768, U.S. Pat. No. 6,690,963, and U.S. Patent Application Publication 2002/0065455, all to Ben-Haim et al., whose disclosures are incorporated herein by reference, describe a system that generates six-dimensional position and orientation information regarding the tip of a catheter. This system uses a plurality of sensor coils adjacent to a locatable site in the catheter, for example near its distal end, and a plurality of radiator coils fixed in an external reference frame. The sensor coils generate signals in response to magnetic fields generated by the radiator coils, which signals allow for the computation of six location and orientation coordinates.
U.S. Pat. No. 6,239,724 to Doron et al., whose disclosure is incorporated herein by reference, describes a wireless, telemetry system for providing coordinates of an intrabody object. The system includes an implantable telemetry unit having (a) a first transducer, for converting a power signal received from outside the body into electrical power for powering the telemetry unit; (b) a second transducer, for receiving a positioning field signal that is received from outside the body; and (c) a third transducer, for transmitting a locating signal to a site outside the body, in response to the positioning field signal.
U.S. Patent Application Publication 2003/0120150, to Govari, whose disclosure is incorporated herein by reference, describes a system wherein a wireless transponder is fixed to an object. The transponder includes at least one sensor coil, in which a signal current flows responsively to electromagnetic fields generated by fixed radiators, and a power coil, which receives a radio-frequency (RF) driving field and conveys electrical energy from the driving field to power the transponder. The power coil also transmits an output signal responsively to the signal current to a signal receiver, which processes the signal to determine coordinates of the object.
U.S. Pat. No. 5,099,845, to Besz et al., whose disclosure is incorporated herein by reference, describes a medical instrument location determining device, which has a radiating element forming part of the instrument to be inserted into an object (such as a human body). The element radiates a signal, which is detected by at least one receiving element. The received signal energy level is used to measure the distance of the radiating element from the receiving element, which is then indicated to an operator of the instrument so that he can locate the instrument within the object.
U.S. Pat. No. 5,762,064, to Polyani, whose disclosure is incorporated herein by reference, describes a medical magnetic positioning system and method for determining the position of a magnetic probe inside the body. At least two spaced magnetometers are fastened to an area on an external portion of the body proximate to the desired location of the probe inside of the body. The three-dimensional magnetic field of the probe is detected at the magnetometers, and the location of the probe is determined in accordance with the location of the detected three-dimensional field.